1. Field of the Invention
The invention relates to a seal arrangement for fuel cells, and, in particular, to a seal arrangement for solid polymer electrolyte fuel cells.
2. Description of Related Art
A fuel cell, such as a solid polymer electrolyte fuel cell, includes a membrane-electrode assembly (MEA) that consists of an electrolyte membrane in the form of an ion exchange membrane, an electrode (anode or fuel electrode) including a catalyst layer and a gas diffusion layer formed on one major surface of the electrolyte layer, and an electrode (cathode or air electrode) including a catalyst layer and a gas diffusion layer formed on the other major surface of the electrolyte layer. A unit cell is constituted by the membrane-electrode assembly (MEA), and one or more separators that form fluid passages through which fuel gas (hydrogen) and oxidizing gas (oxygen, or generally air) are supplied to the anode and cathode and/or channels through which a coolant flows. A laminated structure of at least one unit cell constitutes a module, and a plurality of modules are laminated on each other to provide a set of modules (or a set of cells when the module consists of one unit cell). Terminals, insulators and end plates are disposed on the opposite ends of the set of modules as viewed in the direction of lamination of the cells, so as to provide a fuel cell stack. The fuel cell stack is then fastened at the outside thereof by fastening members (such as tension plates) that extend in the direction of lamination of the cells, such that the modules or cells are fixed together.
In the solid polymer electrolyte fuel cell, a reaction that converts hydrogen into hydrogen ions and electrons occurs at the anode, and the hydrogen ions thus formed move to the cathode through the electrolyte membrane. As a result, a reaction of oxygen, hydrogen ions and electrons produced at the anode of the adjacent MEA and passing through the separator occurs at the cathode. These reactions are expressed as follows:H2→2H++2e− at the anode of the cell2H++2e−+(½)O2→H2O at the cathode of the cell
In the fuel cells, Joule heat is generated, and heat is also generated due to the reactions at the cathode for producing water. To cool the fuel cells, channels that allow a coolant (generally, cooling water) to pass therethrough are formed in the separator for each cell or for a plurality of cells (e.g., two cells).
An example of a seal arrangement for fuel cells is disclosed in Japanese Laid-open Patent Publication No. 2000-182639. In this arrangement, gaskets for sealing coolant channels are provided at surfaces exposed to a coolant, and gaskets for sealing gas passages are provided at surfaces exposed to fuel or oxidizing gas. In the known fuel cell stack, components, such as electrolyte membranes, catalyst layers, gas diffusion layers, adhesive layers, and the like, are disposed in a region of the cells taken in the direction of lamination of the cells, in which region the gaskets are located. Namely, the gaskets overlap the above-mentioned components when viewed in the direction of lamination of the cells.
In the known fuel cell stack, however, the electrolyte membranes, catalyst layers, gas diffusion layers, and the adhesive layers located in the region of the cells overlapping the gasket seal lines in the direction of lamination of the cells are likely to creep when a load to fasten the fuel cell stack is applied. Thus, the materials of the above-indicated components may creep during operation of the fuel cells, which makes it difficult to maintain good sealing property of the gaskets.